Method of manufacturing a plate of electrically insulating material having a pattern of apertures and/or cavities

ABSTRACT

After a plate of electrically insulating, particularly hard and brittle material has been provided with a mask having a very large number of patterned apertures, it is exposed to at least one jet of abrasive powder particles, which jet is moved relative to the plate. In this way a plate is manufactured with a pattern of apertures and/or cavities which are eminently suitable for manipulating electron currents in electronic displays. Plates manufactured in this way may be used, for example, as control plates, spacer plates, or electron transport duct plates in electronic displays.

This is a division of prior application Ser. No. 08/419,977, filed on 7Apr. 1995, now abandoned which is a continuation of Ser. No. 08/029,818,filed on 11 Mar. 1993 now abandoned.

BACKGROUND OF THE INVENTION

The invention relates to a method of manufacturing a plate ofelectrically insulating material having a plurality of cavities and/orapertures arranged in a pattern.

Plates of this type, which may particularly be made of hard, brittlematerials such as glass or ceramic material, are particularly used inluminescent gas discharge displays such as plasma displays, in fieldemission displays, cathode ray displays and in displays in whichelectrons are propagated in ducts having walls of electricallyinsulating material (referred to as insulating electron duct displays)in which the apertures or cavities are used for manipulating electroncurrents. They may be formed as (multi-apertured) control plates andprovided with (addressable) electrodes cooperating with the apertures,as transport plates having a plurality of parallel cavities (transportducts), or as apertured spacers (for example, between a control plateand the luminescent screen of a luminescent display). Further, a use of(thin) wafers of electrically insulating material having a plurality ofperforations is e.g. in pressure sensors.

U.S. Pat. No. 3,956,667 describes a luminescent gas discharge display.This display requires a control plate controlling the individual pixels.This control plate divides the inner space of such displays into twoareas, a plasma area and a post-acceleration area. It comprises aperforated glass plate having an array of lines at one side and at theother side an array of columns of metal conductors or electrodessurrounding or extending along the perforations. These enable electronsto be selectively drawn from the plasma area through the apertures tothe post-acceleration area and to be incident on the luminescent screen.

In the case of a control plate the number of perforations or aperturesin a plate of the type described above is defined by the number ofdesired pixels.

Present-day television line scan patterns use, for example approximately500×700 pixels having a horizontal pitch of 0.5 mm and a vertical pitchof 0.7 mm. These pixels define the pattern of apertures to be providedin the control plate of electrically insulating material. Theseapertures or perforations are conventionally provided by means ofchemical etching (liquid etching, gas phase etching). However, whenstandard materials and chemical etching methods are used, the platethickness, the aperture diameter and the pitch of the apertures cannotbe chosen independently of each other. Moreover, if metal tracks areprovided on the plate to be etched, there is the risk that underetchingof the glass under the tracks may cause the tracks to come loose fromthe glass. It is also difficult to achieve the required accuracy in theuse of chemical etching methods when the plates are relatively thick(thicker than approximately 200 microns, particularly thicker than 400microns).

SUMMARY OF THE INVENTION

It is an object of the invention to provide a (preferably simple) methodof manufacturing a plate which is particularly suitable for the usesdescribed hereinbefore and offers the possibility of setting a largenumber of parameters for providing a desired pattern of cavities and/orapertures in coated (for example metallized) or uncoated plates ofelectrically insulating material.

The method according to the invention is therefore characterized in thatthe pattern is made by means of the following steps:

producing at least one jet of abrasive powder particles;

directing the jet onto a surface of the plate;

limiting the areas where the jet impinges upon the surface;

performing a relative movement between the jet and the plate.

As compared with the state-of-the-art etching processes, the use of sucha powder spraying process for making a pattern of apertures or cavitiesin a plate of electrically insulating material has the advantage that alarge number of parameters is available, inter alia, the type ofabrasive, grain size, diameter of the nozzle emitting the abrasiveparticles, nozzle/plate distance, pressure of the medium with which thepowder particles are transported, movement of the nozzle, speed of therelative movement between nozzle and plate. By varying these parametersit has been found possible to make plates with a pattern of aperturesand/or cavities which comply with the requirements imposed on the use indisplays. The step of changing over from a chemical etching process to apowder spraying process for making patterns having a great many denselyarranged apertures in electrically insulating plates for(electroluminescent) displays appears to lead to a number of unforeseenadvantages in the industrial manufacture of such devices.

To cause the jet to impinge on limited areas only, the jet can be givena limited diameter and moved across the plate for forming a slottedaperture or a duct. The invention provides for the use of a mask if apattern having a large number of small apertures is to be provided. (Theuse of a mask is also advantageous for the formation of theafore-mentioned slotted apertures and ducts.)

The mask used may be formed from, for example a patterned photoresist ora synthetic material.

The use of a perforated (particularly metal) plate as a mask is found tobe very suitable. This plate can be used a number of times in a numberof cases, particularly if it is provided in advance with a protectivecoating.

When a separate metal or synthetic material plate is used as a mask, itis advantageous to stick this mask to the plate to be sprayed. An easilyremovable adhesive can be used for this purpose. An interestingalternative is the use of a plate of a magnetisable metal, for exampleFe for the mask and "sticking" this plate to the plate to be sprayed bymeans of a magnetic field generated at the other side of the plate to besprayed. When an electromagnet is used, the magnetic attraction can beeasily switched on and off.

Sticking is important to maximally prevent the mask from being locallydetached during spraying, causing powder particles to come underneaththe mask and possibly damage the parts not to be sprayed (referred to asunderspraying).

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects of the invention will be apparent from andelucidated with reference to the embodiments described hereinafter.

In the drawing

FIG. 1 is a cross-sectional view of a plate provided with a perforatedmask;

FIG. 2 is a cross-sectional view of a perforated mask provided with aprotective coating;

FIG. 3 is a cross-sectional view of a field emission display;

FIG. 4a is an elevational view and

FIG. 4b is a cross-sectional view of an insulating electron ductdisplay;

FIG. 5 is a cross-sectional view of a gas discharge display;

FIG. 6 is an exploded view of a flat panel display;

FIGS. 7 and 8 show diagrammatically how a pattern of apertures isprovided in a plate by means of a powder spraying device;

FIGS. 9a, 9b and 9c show various patterns of apertures realised in thismanner.

FIGS. 10a, 10b, 11a and 11b show, in cross section, communicatingcavities formed from opposite side of plates.

FIG. 12 shows diagrammatically how a spray nozzle may be rotated about afixed point.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Electrically insulating control plates, transport plates and/or spacerplates having very accurate patterns of apertures and/or cavities arerequired for use in different types of (electroluminescent) displays.The plate thickness may be between 200 and 5000 microns, particularlybetween 200 and 700 microns. The depths of the apertures or cavities mayrange between 50 and 5000 microns. A characteristic material for theseapplications is glass or ceramic material.

FIG. 1 is a cross-sectional view of such a plate 1 provided with a metalmask 2. Suitable metals are those which are easily etchable. A mask ofFe is slightly attacked by the abrasive powder spraying process used inaccordance with the present invention to provide apertures 3 in theplate 1. An alternative material is (stainless) steel or an invar alloy(NiFe). Instead of a metal mask, which has the advantage that it can beused several times (for example, several dozen times), a lacquer mask(for example, a lacquer used in the silk-screening technique) or asynthetic material mask (for example, an UV-sensitive syntheticmaterial) can be used.

The metal mask 2 may be provided with a protective coating 4 (FIG. 2)of, for example electrolytically provided nickel or chromium or ofvapour-deposited aluminium. A coating of a synthetic material mayalternatively be provided. A loose mask can be stuck on the plate 1 bymeans of an adhesive layer 5 so as to inhibit local detaching during thepowder spraying process. The adhesive layer 5 may comprise an adhesivewhich is soluble in water (for example, an adhesive based on glucose).Such an adhesive can be easily provided at low cost and simply removedafter use. The mask 2 may be alternatively made of a magnetic materialand "stuck" to the plate 1 by means of a magnetic field.

The apertures 3 denoted by broken lines in the plate 1 are slightlytapered in the embodiment of FIG. 1. When plates are used as internalvacuum supports (spacer plates) in field emission displays, such anaperture shape is not unusual for making cylindrical apertures orcavities with parallel walls. Plates having cylindrical apertures aresuitable, for example, as spacers between a control plate and theluminescent screen in an insulating electron duct display.

FIG. 3 is a diagrammatic cross-sectional view of a field emissiondisplay comprising a substrate 40, conical emission tips 41, a spacerplate 42 with apertures 43 and a front wall 45 with a luminescent screen44. The spacer plate 42 may advantageously be made by means of themethod according to the invention.

FIG. 4a is a diagrammatic elevational view and FIG. 4b is across-sectional view of an insulating electron duct display 6 asdescribed in EP-A-400 750. This display comprises a plurality ofinsulator plates 10a, 10b, 10c, 10d having regular aperture patternsbetween a transparent face plate 7 and a rear wall 14.

A luminescent screen 15 is provided on the inner surface of the faceplate 7. A flu-spacer plate 10d having a characteristic thickness ofapproximately 1 mm and, for example 1×10⁶ apertures corresponding to thenumber of luminescent areas (colour dots) on the screen 15 is adjacentto this luminescent screen. The colour dots are addressed by means of apreselection plate 10a and a fine-selection plate 10c each of, forexample glass and being 0.5 mm thick. The plate 10c has a pattern ofaperture triplets R, G, B in this case. The apertures in the plate 10care activated, for example row by row by means of metal fine-selectionelectrodes 13, 13', 13", . . . . These electrodes may be provided afterthe apertures have been made, which provides the possibility ofmetallizing the walls of the apertures as well. An alternative method isto provide the fine-selection electrodes in advance. Preselection plate10a is separated from fine-selection plate 10c by a spacer structure10b, in this case a plate having (large) apertures connecting each oneof, for example 350,000 apertures 8, 8', . . . in the preselection plate10a with a plurality of apertures in the fine-selection plate 10c. Thepreselection plate 10a is provided with preselection electrodes 9, 9', .. . for activating, for example row by row the apertures 8, 8', . . .communicating with electron transport ducts 11, 11', 11", . . . (seealso FIG. 4a). The transport ducts 11, 11', 11", . . . are separatedfrom each other in this case by electrically insulating partitions 12,12', 12", . . . . An alternative method is to provide the transportducts (a total number of several hundred, for example 200 or 400) asduct-shaped cavities having a depth of several mm and a width of, forexample 0.5 or 1 mm in the rear wall 14. The method according to theinvention is also applicable for this purpose. The rear wall 14constitutes an electron transport plate in this case. The transportducts 11, 11', 11", . . . cooperate, via a perforated cathode plate 16(of, for example 1 mm thick glass) with a-line-shaped-electron source18. The apertures 17 in the cathode plate 16 (also several hundred, forexample 200 or 400) may also be provided advantageously by means of themethod according to the invention.

In connection with the large number of perforated, relatively thickplates (at least four), the very large numbers of apertures, thenecessity of a continuous or strip-shaped coating on a plurality ofthese plates, the invention also facilitates the manufacturer of"insulating electron duct displays" of the type shown in FIGS. 4a and 4bon an industrial scale.

FIG. 5 is an elevational view of a gas discharge display as described inDE-2 412 869 , corresponding to U.S. Pat. No. 3,956,667. This displayhas an insulator plate 21 provided with a regular pattern of apertures22. Row conductors 23 extend at one side across the apertures 22. Theseconductors are provided by means of, for example a printing technique,vapour deposition or photolithography. Column conductors 24 extendacross the other side of the apertures 22. DE-2 412 869 is referred tofor the operation of such a display. The insulator plate 21 mayadvantageously be made by means of the method according to theinvention.

FIG. 6 is an elevational view of a flat panel display as presented inpublications by MEI. This display comprises a large number of metalelectron beam control electrodes 25, 25', 25", . . . provided withslotted apertures between a rear wall 26 and a luminescent screen 27.These electrodes can be provided by means of the invention on a plate ofelectrically insulating material having the same aperture pattern, whichhas great advantages as regards ease of handling and suspension.

FIG. 7 shows a plate 28 to be sprayed, which plate is positioned on asupport 29. The support 29 is movable in the direction of the arrow Pperpendicular to the plane of the drawing. The plate 28 is provided witha mask 30 having the shape of a perforated metal plate. In this examplethe mask 30 has a regular pattern of circular apertures (see FIG. 8). Adevice 31 for performing an abrasive operation (powder spraying device)is shown diagrammatically as a spraying unit 32 having a nozzle 33directed onto the surface of the plate 28. Dependent on whetherapertures or cavities are to be made, the nozzle/mask distance may rangebetween 0.5 and 25 cm, typically between 2 and 10 cm. During operation ajet of abrasive powder particles, for example silicon carbide particles,aluminium oxide particles, granulated glass or steel or mixtures thereofis blown from the nozzle 33. A pressure principle or a venturi principlemay be used for this purpose. Abrasive particle dimensions suitable forthe object of the invention range between 1 and 200 microns, typicallybetween 10 and 100 microns.

In this embodiment spraying unit 32 with nozzle 33 can be traversed in adirection transverse to the arrow P by means of a traversing device 34which has a spindle 35.

Stops provided with electric contacts are denoted by the referencenumerals 36 and 37 and are assumed to be connected to a reversingcircuit so as to reverse the sense of rotation of the spindle 35 to bedriven by a motor.

During operation the support 29 and the plate 28 make a, for examplereciprocating movement parallel to the X axis and the spraying unit 32performs axial traversing movements parallel to the Y axis (FIG. 8), thespeeds of movement being adapted to each other in such a way that thecomplete desired aperture or cavity pattern is obtained in the plate 28.Instead of one nozzle it is possible (for example, for the purpose ofaccelerating the process) to use a number of nozzles for spraying areaswhich are spaced apart, are tangent to each other, or partially orcompletely overlap each other.

FIG. 9a shows in real size a part of a pattern of circular aperturesobtained in this manner.

FIGS. 9b and 9c show patterns of slotted apertures obtained in similarmanners.

A 0.5 mm thick plate of 30×40 cm can be provided with a very accurateaperture pattern of 1×10⁶ apertures having a diameter of 600 micronswithin 5 minutes in the manner described above.

For insulating electron duct displays of the FIG. 4 type, fourperforated plates are required, with aperture patterns having a numberof apertures varying between 100×10³ and 10×10⁶.

The invention may alternatively be used for providing a large number ofparallel elongate cavities in a plate of electrically insulatingmaterial, which cavities are used as electron transport ducts in aninsulating electron duct display. The display shown in FIG. 4a comprisesseveral hundred (for example, 400) of such electron transport ductcavities 11, 11', 11", . . . etc.

The invention is not only suitable for unilaterally providing a patternof apertures or cavities but also for providing patterns of cavities atboth sides. The cavities can be provided in such a way that theycommunicate with one another, for example each cavity at one side of aplate 1 communicates with two or more cavities at the other side of aplate 1 (FIG. 10a) or each cavity at one side communicates with onecavity (equally large as the first cavity, or different in size) at theother side (FIG. 10b). This provides the possibility of manufacturingone plate 1 that serves as two. This results in a greater ease ofhandling during the manufacturing process.

FIGS. 11a and 11b show how one plate 1 that serves as three can be made.First, a sub-pattern of cavities is made in each one of the facingsurfaces of the plate 1 through masks 2a and 2b, which cavities do notcommunicate with one another (FIG. 11a). In a subsequent powder sprayingstep, in which a mask 2c arranged on one of the surfaces is used,corresponding cavities are connected to each other by providingperforations (FIG. 11b).

It is to be noted that duct-shaped cavities, as previously mentioned inconnection with the construction of FIG. 4, can be made without using amask, for example by producing at least one localized powder jet and bymoving it once or a number of times across the plate at the locationwhere the duct is to be made.

If the powder spraying process is performed at a relatively high speed("high-speed spraying"), it is preferable to cool the metal mask bycooling, for example the glass plate by means of a flow of liquid.Heating of the metal mask may alternatively be inhibited by using asynthetic material coating which ensures that the powder particles notpassing through the apertures rebound more or less elastically.

In the powder spraying process the shaping of the apertures may beenhanced if the plate to be sprayed is supported by a plate having apattern of apertures which is exactly located under the aperture patternto be sprayed. The plate to be sprayed may alternatively be supported atits edges only, at locations where it is not apertured.

When using a nozzle which is substantially perpendicular to the platesurface, apertures having slightly tapering walls will be obtained.Dependent on the geometries used, the walls may extend at an angle ofbetween several degrees and 20 degrees to the normal on the platesurface. The taper may be limited by performing the abrasion processfrom both plate surfaces.

Apertures (and cavities) having walls which are transverse to the platesurface can be obtained within the scope of the invention by causing anozzle, which is arranged obliquely to the surface, to rotate about afixed point during the powder spraying process so that it describes, forexample, a surface of a cone. To this end the nozzle (the spray pipe) 38can be placed in a holder having a point of rotation M and rotated withthe aid of a template arranged above this holder. See FIG. 12.

An alternative to the above-mentioned method is the use of a pluralityof stationary nozzles which are arranged in such a way that during thepowder spraying process the object is sprayed from different directionsat an angle to the normal on the object surface. Suitable results wereachieved, for example, with six nozzles placed at the vertices of aregular hexagon, with each nozzle in a plane parallel to one of thesides of the hexagon and extending at an angle α to the normal on theobject surface. In most cases an angle α of between 10° and 50° wassatisfactory for obtaining cavities and/or apertures having wallsextending transversely to the object surface.

Plates manufactured by using the inventive method may contain at leastone and in most cases a very large number of holes (and/or cavities)which are placed close together so that they constitute at leastapproximately 30% or even more than approximately 50% of the exposedsurface area of the plate. As mentioned already areas of utility are,amongst, others various types of electronic displays where plates havingarrays of e.g. one hundred thousand, several hundred thousands, or moreholes are utilized to control electron propagation. Other areas ofutility are e.g. electron tubes of the image intensifier type where theoutput electrons are directed towards a phosphor surface which emitslight upon being struck by electrons, or where the output electrons arebeing utilized directly, e.g. for the exposure of a photographic film.

What is claimed is:
 1. A method of forming in a plate of electrically insulating material a multiplicity of precisely-positioned passages between opposite first and second sides of the plate, said method including the steps of:a. adhesively attaching to at least one of the sides of the plate a mask having apertures located at predefined areas where the passages are to be formed; b. producing at least one let of abrasive powder particles; c. directing the at least one jet at a surface of the mask to effect abrasion of the electrical insulating material through the apertures of said mask; and d. moving at least one of the plate and the at least one jet relative to the other to effect formation of the passages at the predefined areas; where the passages comprise:cavities in the first side of the plate formed by directing the at least one jet of abrasive powder particles at a first mask attached to said first side; and cavities in the second side of the plate formed by directing the at least one jet of abrasive powder particles at a second mask attached to said second side; at least one of the cavities in the first side communicating with a plurality of the cavities in the second side.
 2. A method of forming in a plate of electrically insulating material a multiplicity of precisely-positioned passages between opposite first and second sides of the plate, said method including the steps of:a. adhesively attaching to at least one of the sides of the plate a mask having apertures located at predefined areas where the passages are to be formed; b. producing at least one jet of abrasive powder particles; c. directing the at least one jet at a surface of the mask to effect abrasion of the electrical insulating material through the apertures of said mask; and d. moving at least one of the plate and the at least one jet relative to the other to effect formation of the passages at the predefined areas; where the passages comprise:cavities in the first side of the plate formed by directing the at least one jet of abrasive powder particles at a first mask attached to said first side; and cavities in the second side of the plate formed by directing the at least one jet of abrasive powder particles at a second mask attached to said second side; at least one of the cavities in the first side communicating with
 3. A method as in claim 1 or 2 where at least one of the passages comprises an intermediate aperture in a midsection of the plate formed, after forming the cavities in one of the first and second sides, by directing at least one jet at a third mask attached to said side, said intermediate aperture connecting one of the cavities in the first side with one of the cavities in the second side.
 4. A method as in claim 1 where the mask comprises a radiation-sensitive synthetic material.
 5. A method as in claim 1 where the mask is attached to the plate by means of a readily-removable adhesive.
 6. A method as in claim 5 where the adhesive is water soluble.
 7. A method as in claim 6 where the adhesive comprises glucose.
 8. A method as in claim 1 where the mask comprises a metallic material having a protective coating on a side of the mask which is exposed to the at least one jet of abrasive powder particles.
 9. A method as in claim 8 where the protective coating comprises a material selected from the group consisting of nickel, chromium and aluminum.
 10. A method as in claim 8 where the protective coating comprises a synthetic material for effecting elastic rebound of the abrasive powder particles.
 11. A method as in claim 1 where the at least one jet of abrasive powder particles is directed obliquely at the surface of the mask.
 12. A method of forming in a plate of electrically insulating material a multiplicity of precisely-positioned passages between opposite first and second sides of the plate, said method including the steps of:a. adhesively attaching to at least one of the sides of the plate a mask having apertures located at predefined areas where the passages are to be formed; b. producing at least one jet of abrasive powder particles; c. directing the at least one jet at a surface of the mask to effect abrasion of the electrical insulating material through the apertures of said mask; and d. moving at least one of the plate and the at least one jet relative to the other to effect formation of the passages at the predefined areas; where the at least one jet of abrasive powder particles is directed obliquely at the surface of the mask and is rotated to describe a conical surface.
 13. A method as in claim 1 where the at least one jet of abrasive particles comprises a plurality of said jets produced by respective nozzles aimed in different directions.
 14. A method as in claim 13 where the nozzles are positioned at vertices of a polygon.
 15. A method as in claim 14 where the polygon comprises a hexagon.
 16. A method as in claim 13 where the plurality of jets overlap each other.
 17. A method as in claim 1 where the movement of the plate and the at least one jet relative to the other is performed by scanning said at least one jet of abrasive powder particles over the mask. 